An experimental and analytical study of heat and noncondensing water vapor transport in a vertical porous plane wall subject to air filtration.

摘要

A novel approach to building ventilation, commonly referred to as permeodynamic insulation, consists of forcing air through the porous insulation contained within the walls and/or ceiling of a building. Compared with conventional ventilation techniques, a lower rate of heat loss has been claimed for buildings equipped with permeodynamic insulation systems.;This work studied the energy saving potential for permeodynamic insulation and provided information on the steady-state heat and noncondensing water vapor transport processes within a vertical porous wall. Wall surfaces were exposed to different environments and subjected to various rates and directions of air filtration. Two vertical walls, joined by horizontal impermeable adiabatic surfaces, simulated a two-dimensional enclosure. Distributions of temperature and water vapor concentration in a vertical porous plane wall, with a thickness to height ratio of 14.3, were predicted with a one-dimensional analytical model and measured using an ASTM C 976-82 calibrated hot box.;Temperature and water vapor concentration profiles were nonlinear with good quantitative agreement between theory and measurements for large rates of air filtration. At low rates of air filtration, experimental distributions of temperature and water vapor concentrations were highly two-dimensional with significant deviations from one-dimensional predictions. This phenomenon was attributed to natural convection induced motion. High humidity experiments showed that condensation could be prevented by filtrating moist air through the porous wall from the cold dry environment to the warm moist side.;Predictions and measurements indicated a lower rate of heat input, optimized at a particular rate of air filtration, for an enclosure ventilated with porous walls as compared to one with nonporous walls ventilated by open vents/cracks.